If it is a round butt, then the Hogue 500 X Frame Tamers should work. This is the grip used on the S&W 500 and it has a covered back strap. Here's a link
https://www.hogueinc.com/handgun-gri...wesson/xzframe
Here's a picture mounted on my 66-8 round butt.
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If those don't work, you'll probably have to go custom -- Herrett Jordan Troupers maybe.
Paul